1. Field of the Invention
The present invention relates to an air-conditioner and, more particularly, to a method for controlling operations of an air-conditioner.
2. Description of the Background Art
In general, an air-conditioner is a device for conditioning a certain space to a temperature, humidity and air flow distribution suitable for humans' activity and cooling a room by using a principle of evaporation heat of taking ambient heat when a high temperature high pressure-compressed refrigerant is evaporated through various types of compressors to remove dust or the like in the air. As the refrigerant, a liquid that can be easily evaporated at a low temperature is used, and usually, a freon gas is used.
FIG. 1 is a block diagram showing the construction of a conventional air-conditioner.
As shown in FIG. 1, the conventional air-conditioner includes a controller 10 for measuring an indoor temperature and outputting a control signal for controlling a cooling capacity on the basis of the measured temperature and a pre-set temperature; a compressor 20 for compressing a refrigerant on the basis of the control signal; a condenser 30 for condensing the compressed refrigerant; an expansion valve 40 for expanding the condensed refrigerant; and an evaporator 50 for evaporating the expanded refrigerant.
An operational principle of the conventional air-conditioner will now be described.
First, the controller 10 measures an indoor temperature and outputs the control signal for controlling a cooling capacity on the basis of the measured indoor temperature and the temperature previously set by a user.
The compressor 20 includes a first compressor 21, a small capacity compressor, and a second compressor 22, a large capacity compressor. The first compressor 21 can vary a compression capacity to control a cooling capacity according to the control signal, and the second compressor 22 has a constant compression capacity. The second compressor 22 is a constant-speed compressor.
The first and second compressors 21 and 22 are selectively driven according to the control signal to compress the refrigerant to a high temperature high pressure. Namely, the compressor 20 operates in three types of modes: when only the first compressor is driven, only the second compressor is driven, and both first and second compressors are driven, to thereby change a compressing capacity of the refrigerant required for air-conditioning.
The range of controlling the cooling capacity differs depending on the types of the first and second compressors. The constant speed type compressor has a constant operation speed, so it controls an operation frequency an indoor temperature by being turned on/off. The inverter compressor is controlled in its operation speed, so it can control an indoor temperature relatively precisely by controlling an operation frequency.
For instance, if a compressing capacity of the air-conditioner is total 100, in which the first compressor 21 is an inverter compressor having a compressing capacity of 40 and the second compressor 22 is a constant-speed compressor having a compressing capacity of 60, an air-conditioner employing the first and second compressors can control indoor temperatures with compressing capacities of 10, 20, 30, 40, 50, 60, 70, 90 and 100 relatively precisely.
Recently, an air-conditioner employing 4 compressors is used. Its operation is the same as the compressor of FIG. 1, and capacities of compressors are 20, 20, 30 and 300 or the same compressors are used.
An air-conditioner employing two compressors will now be described as an example.
The condenser 30 condenses the refrigerant which has been compressed to a high temperature high pressure in the compressor 20, and the expansion valve 40 expands the condensed refrigerant. The evaporator 50 evaporates the expanded refrigerant, taking heat around it, whereby heat exchange is made that a temperature of air contacting with the surface of the evaporator 50.
The conventional air-conditioner having the inverter compressor and the constant-speed compressor is used to control a cooling capacity by using the inverter compressor and the constant-speed compressor, so that it can control the cooling capacity precisely according to air-conditioning operation load.
The method for controlling operations of the air-conditioner having the inverter compressor and the constant-speed compressor will now be described with reference to FIGS. 2A and 2B.
FIGS. 2A and 2B are a flow chart of the method for controlling operation of the air-conditioner having the inverter compressor and the constant-speed compressor in accordance with the conventional art.
As shown in FIGS. 2A and 2B, the method for controlling operations of conventional air-conditioner having the inverter compressor and the constant-speed compressor, including: a step (S21) in which whether an operation load of the air-conditioner is increased is determined; a step (S22) in which when the operation load is increased, an operation frequency of the inverter compressor is lowered to a minimum frequency of the inverter compressor and the constant-speed compressor is operated, and then, a compressing capacity of the air-conditioner is adjusted to be equal to a compressing capacity corresponding to the operation load by increasing the operation frequency of the inverter compressor in order to maintain a pre-set temperature; and a step (S23) in which when the operation load is reduced, the operation frequency of the inverter compressor is increased to a maximum frequency of the inverter compressor and the constant-speed compressor is stopped, and then, the compressing capacity of the air-conditioner is adjusted to be equal to the compressing capacity corresponding to the operation load by reducing the operation frequency of the inverter compressor in order to maintain the pre-set temperature.
The method for controlling operations of the air-conditioner having the inverter compressor and the constant-speed compressor in accordance with the conventional art will now be described in detail.
The conventional air-conditioner having the inverter compressor and the constant-speed compressor determines whether its operation load is increased (step S21). That is, the air-conditioner determines whether the operation load is increased by comparing its outputted compressing capacity and a compressing capacity corresponding to the operation load.
When the operation load is increased, the operation frequency of the inverter compressor is lowered to the minimum frequency of the inverter compressor and the constant-speed compressor is operated, and then, a compressing capacity output of the air-conditioner and the compressing capacity corresponding to the operation load are adjusted to be equal by increasing the operation frequency of the inverter compressor (step S22).
Namely, when the operation load of the inverter compressor is increased, the compressing capacity of the air-conditioner and the compressing capacity corresponding to the operation load of the inverter compressor are compared (step S22-2) while increasing the operation frequency of the inverter compressor (step S22-1). Herein, when the compressing capacity of the air-conditioner becomes equal to the compressing capacity corresponding to the operation load of the inverter compressor, the operation frequency which has been increased as much as a predetermined level is maintained as it is.
If, however, the outputted compressing capacity of the air-conditioner is different from the compressing capacity corresponding to the operation load of the inverter compressor, it is determined whether the operation frequency of the inverter compressor is the maximum frequency of the inverter compressor (step S22-3). If the operation frequency of the inverter compressor is the maximum frequency, the operation frequency of the inverter compressor is reduced to the minimum frequency (step S22-4), and then, the constant-speed compressor is operated (turned on) (step S22-5).
In the state that the constant-speed compressor is being operated after the operation frequency of the inverter compressor is reduced to the minimum frequency, the outputted compressing capacity of the air-conditioner is adjusted to be equal to the compressing capacity corresponding to the operation load while increasing the operation frequency of the inverter compressor by as much as certain levels (step S23). Namely, after the constant-speed compressor is operated, while the operation frequency of the inverter compressor is increased by as much as certain levels (step S23-1), the outputted compressing capacity of the air-conditioner is adjusted to be equal to the compressing capacity corresponding to the operation load (step S23-2).
Meanwhile, when the operation load is reduced, the operation frequency of the inverter compressor is increased to the maximum frequency of the inverter compressor and the constant-speed compressor is stopped, and then, the outputted compressing capacity of the air-conditioner is adjusted to be equal to the compressing capacity corresponding to the operation load by reducing the operation frequency of the inverter compressor (step S24).
Namely, when the operation load is reduced, while the operation frequency of the inverter compressor is being reduced by as much as certain levels (step S24-1), the outputted compressing capacity of the air-conditioner and the compressing capacity corresponding to the operation load are compared (step S24-2). If the two compressing capacities are equal, the operation frequency which has been increased as much as the certain level is maintained as it is.
If, however, the outputted compressing capacity of the air-conditioner is different from the compressing capacity corresponding to the operation load of the inverter compressor, it is determined whether the operation frequency of the inverter compressor is the minimum frequency (step S24-3). If the operation frequency of the inverter compressor is the minimum frequency, the operation frequency of the inverter compressor is increased to the maximum frequency (step S24-4). Thereafter, the constant-speed compressor is stopped (turned off) (step S24-5).
In the state that the constant-speed compressor is stopped after the operation frequency of the inverter compressor is increased to the maximum frequency, the outputted compressing capacity of the air-conditioner is adjusted to be equal to the compressing capacity corresponding to the operation load by increasing the operation frequency of the inverter compressor by as much as certain levels (step S25). After the constant-speed compressor is stopped, the outputted compressing capacity of the air-conditioner is adjusted to be equal to the compressing capacity corresponding to the operation load (step S25-2) by reducing the operation frequency of the inverter compressor by as much as certain levels (step S25-1).
Herein, the sum of the compressing capacity of the inverter compressor and the outputted compressing capacity of the constant-speed compressor, namely, the capability of varying the outputted compressing capacity of the air=conditioner to be equal to the compressing capacity corresponding to the operation load is called an operation load coping capability. Accordingly, it is ideal that the relation between the outputted compressing capacity of the air-conditioner and the compressing capacity corresponding to the operation load has a form of y=x graph.
However, the method for controlling operations of the air-conditioner having the inverter compressor and the constant-speed compressor in accordance with the conventional art has the following problems.
That is, in the process of switching from the inverter compressor to the constant-speed compressor, namely, when the constant-speed compressor is operated after the operation frequency of the inverter compressor is reduced to the initial frequency or when the constant-speed compressor is stopped after the operation frequency of the inverter compressor is increased to the maximum frequency, the compressing capacity of the operation load changes, so the compressing capacity of the air-conditioner fails to change accordingly to the compressing capacity corresponding to the operation load. Thus, the operation load coping capability, degrading refreshingness (agreeable atmosphere) in a room.
In addition, since the load of the air-conditioner is rapidly changed before and after the inverter compressor and the constant-speed compressor are switched, they cannot be stably switched.